Method of determining inequalities in wall thickness of tubes



- 4 1, June 14, 1927. F. A. RD 632 Q76 METHOD OF DETERMINING INEQUALITIES IN WALL THICKNESS OF TUBES Filed Avril 22, 1925 r so in any cross sectlon isuniform;

Patented .1... 14, 1927.

UNITED STATES- PATENT OFFICE. I

FRANCIS A. HUBBARD,- OI' WYOMING, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 01' NEW YORK, N. 'Y., A CORPORATION 01' NEW YORK.

METHOD OI DETERMINING INEQ UAIIITIES IN WALL THICKNESS OI TUBES.

Application fled April 22, 1925. Serial No. 24.848

This invention relates to a method of de-. termining the variations in thickness of the walls of metallic tubes or ipes and more especially to a method of etermining the variations in thickness of the sheath of lead covered cable.

Heretofore, in sheathing cables with lead, trouble has been experienced due to the core being eccentric with the sheath as it comes 1 from the lead press. To overcome this trou-v ble it has lieen necessar to use a sufficiently thick lead coating so that when the thick ness varied, the minimum coating obtained would be suflicient forv all purposes.

The present invention, by determining the variations in the sheath thickness as the cable comes from the lead press, afi'ords a means of effecting considerable saving in the amount of lead used since any variation can immediately be taken care of by adjusting the temperature of the molten lead and the normal thickness of the lead sheath thereby decreased.- I

To accom lish this, the present invention makes use 0 the distribution of current in a conductor, the cross section of which is not symmetrical. It is well known that electric current in such a conductor will distribute itself in such a way that the current density in other words, the' amount of current flowing in any part is proportional to thethi knees of that part. The distribution of the J agnetic field I about sucha conductor will correspond with I the distribution of thecurrent in that section.

If the current passing through the conductor is alternating, the

magnetic field will also alternateand coils of wire introduced into this magentic field will have voltages induced in them, the strength of which will de nd u on 'the strength of the ma tic p; P s

It has been found that alternatin current 6 having a relatively low frequency, or'exam ple cycles is best suited for this urpose. A measure of the voltage in the coi introduced into the field will determine the asymmetry in the thickness ofthe conductor in W ea h i n.

This method will be better understood from the following description taken inconnection with the attached drawing in which Fig. '1 shows a general schematic view of the method of applying alternating current to the cable sheath and the general arrangement of the detecting coils, while Fig.2 shows on a larger scale and in somewhat more detail the apparatus used. I Referrmg to Fig. 1, the lead press is designated by 1 from which is being extruded lead covered cable 2. A source of alternate 1ng current 3 impresses on cable 2a current having a frequency of approximately 60 cycl'es. One wire from this source is attached to the outlet 4' of the lead ress so that electrlcal connection is made etween this wire and the cable, the other wire being connected to the cable by means of a contact at some point such as 5.

Two exploring coils 6 and 6 having cores 7 and 7 and coils of wire 8 and 8', respectively, are placed adjacent the outlet of the lead press and are arranged sothat the may be moved aboutthe cable in either direction approximately 180 degrees. The current induced in the exploring coils is ampllfied in the well known manner by amplifiers represented by 9 and 9 (Fig. 2) and then rectlfied by rectifiers-lO and 10. The corresponding rectified currents then pass throu h electromagnetic devices 11 and 11'. 7 place adjacent each other and having a common armature 12 between them as shown in Fig. 2. This armature is ivoted at14: and coacts with a scale 13. Fig. 1, the amplifier, rectifiers, and detector are represented generally at 17. In 0 eration, the alternating current, as pointe out above, passes through the sheath, sets up a magnetic field about the sheatlrwhich magnetic field induces voltages in'the ex loring coils. If the thickness of the sheath is uniform so that voltages of equal intensity are'set up in the exploring coils, magnets 11 and 11 (Fig. 2) will be energized with equal currents and since these magnets are identical, $0 attractive forces exerted on armature 12 will be equal,

, so at he rm re tha d the 19 voltages of greater magnitude t stillbe or visible sign appended claims.

ointer will be at the midpoint of the scale. 1?, however, the cable sheath 2 is thicker in the upper portion, as shown in Fig. 2, more current wil flow in this section increasing the magnetic field near it inducin in coil 6, an those induced in coil 6. These induced voltages are amplified and rectified and pass through the windings of magnets 11 and 11'. The current passing through magnet 11 being greater than that passing through magnet 11', the force exerted on armature 12 by magnet 11 will be greater than that exerted by magnet 11' and hence the armature will be attracted'toward magnet 11 causing the pointer to move to the-upper section of scale 13. This indicates that the sheath of the cable is thicker at the top than at the bottom. The amount that the pointer moves will give an indication of the difierence in thickn r To give a further indication of the eccentricit of the sheath, a si nal ma be introduce between the amplifiers an rectifiers.

This is accomplished by bridging across the outlets of the amplifiers 9 of a differential transformer 16. The secondary winding 17 of this transformer is connected to any suitable signal which may be either audible or visible. In the drawing, a telephone receiver is indicated. However, a bell or a lamp or both may be inserted in this secondary winding to ive the required signal.

The primary windings 15 and 15' are ar-' ranged to o pose so that when currents of equal intensities are flowi in these windings, no current is induced in the secondar winding and hence no signal is given. I

however, the cable thickness is not uniform,

the current in either primary winding 15 or l5 will be the greater and a current will induced in the secondary winding. This unbalance is ev1ldenced by either the audible It is realized that many modifications may be made of the apparatus here shown and with n the spirit of this invention which 1s llmited only by the scope of the What is claimed is:

1. In combination, a metallic tube, a ci-rd cuit including a source of alternating current and said tube, exploring'coils located in the magnetic field produced thereby, and means connected to said coils for detecting the agmmetry of the thickness of the wall of am tube.

2., combination, a .metallic tube, a circuit mcludmg'a source of alternating current and said tube,'explo coils located in the magnetic field pi tfiiced thereby, means for amplifying and rectifying the voltages induced in said coils, and means oon ec edw nd ce ls for md e g the and 9', the pri-' detecting, devices introduced into the magnetic field produced around said tube, and means for determining which of said detecting devices is in the maximum intensity of magnetic field strength. I

4. In a device if the character described, in combination, a metallic tube, means for im ressing alternating current on said tube, and means for locating the section of estbe magnetic field intensity surrounding said tu 5. In a device of the character described, in combination, a metallic tube means for determinin the asymmetry of the thickness of the wal thereof comprising an alternating current source connected to said tube coils ocated in the magnetic field produced thereby, and an indicating device connected thereto '-for determining the asymmetry in the wall thickness.

6. In a device of the character described in combination, a metallic tube, a source oi alternating current connected in circuit duced in said coils by sa1d-magnetic field,

a differential transformer mary' windings connected to said co 1.18, and an indicator connected to the secondary of said transformer.

having its prigreat 1 8. A method of determining the asymmetry of the wall thickness Of a tube comprising passin an alternating current through the tu inserting detecting devices 1n the magnetic fields surrounding the tube, and indicating which offlsaid detecting evices is in the maximum. strength magnetic field.

'9. A- method of determining the asymmetry of the wall thickness of a metallic tube comprisin passing an alternat-in current through Ihe tube, inserting co of. wire in the magnetic field surroundirg; said tube, and determining .which of sai coils has the larger voltage induced therein.

10. A method of determini the asymmolairy of the wall o a metallic tu com r' passmg' a ternati current through tube, inserting coils 0 wire in the magnetic field set up by said alternating current around said tube, am lifying and rectifying the voltages induce in the coils of wire, passing the resultant currents through electromagnets exerting differential attractive forces on a common armature, and indicating wlnchof said electromagnets exerts the greatest force on said armature,

and indicating also the amount by which the force exerted by one electromagnet exceeds the force exerted by the other.-

In witness whereof, I hereunto subscribe my name this 17th day of April, A. D. 1925.

FRANCIS A. HUBBARD. 

